Valve device and system in which the valve device is mounted

ABSTRACT

A valve device that includes a valve body; a valve shaft configured to rotate the valve body; a coil spring being electrically conductive and configured to be twisted with rotation of the valve body and the valve shaft; a first conductive member being electrically conductive and facing an inner circumferential surface or an outer circumferential surface of the coil spring in a radial direction of the coil spring; and a first detector configured to detect at least one of a rotation angle of the valve body or a rotation angle of the valve shaft based on an electrostatic capacitance between the coil spring and the first conductive member, the electrostatic capacitance changing according to a state of the coil spring that changes with the rotation of the valve body and the valve shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2019-204893, filed on Nov. 12, 2019, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a valve device and a system in whichthe valve device is mounted.

BACKGROUND

Japanese Patent Application Publication No. 2019-124527 describes athrottle valve. The throttle valve of Japanese Patent ApplicationPublication No. 2019-124527 includes a rotary body and a coil spring(return spring) configured to be twisted with rotation of the rotarybody. Japanese Patent Application Publication No. 2019-124527 furtherdescribes a rotation angle detector. The rotation angle detectordescribed in Japanese Patent Application Publication No. 2019-124527includes a rotary body, a rotor disposed coaxially with the rotary body,a rotary conductive member disposed coaxially with the rotor at one endof the rotor, a fixed conductive member disposed to face the rotaryconductive member, and an electronic circuit configured to detect arotation position of the rotary body based on a change in an inductancebetween the rotary conductive member and the fixed conductive memberaccording to a position of the rotary conductive member in its rotationdirection.

SUMMARY

In the technique of Japanese Patent Application Publication No.2019-124527, the rotary conductive member and the fixed conductivemember need to be disposed to detect the rotation position of the rotarybody, which may cause the rotation angle detector to become oversizedand complicated. In view of this, the disclosure herein provides artthat enables a valve device to determine a rotation angle whilepreventing the valve device from becoming oversized and complicated.

A valve device disclosed herein may comprise: a valve body; a valveshaft configured to rotate the valve body; a coil spring beingelectrically conductive and configured to be twisted with rotation ofthe valve body and the valve shaft; a first conductive member beingelectrically conductive and facing an inner circumferential surface oran outer circumferential surface of the coil spring in a radialdirection of the coil spring; and a first detector configured to detectat least one of a rotation angle of the valve body or a rotation angleof the valve shaft based on an electrostatic capacitance between thecoil spring and the first conductive member, the electrostaticcapacitance changing according to a state of the coil spring thatchanges with the rotation of the valve body and the valve shaft.

This configuration enables detection of at least one of the rotationangle of the valve body or the rotation angle of the valve shaft byusing a change in the electrostatic capacitance between the coil springand the first conductive member in response to rotation of the valvebody and the valve shaft. In realizing the configuration for determiningthe rotation angle in the valve device, the above configuration enablesdetection of the rotation angle by using the coil spring that is twistedwith the rotation of the valve body and the valve shaft without anyadditional configurations such as a rotary conductive member and a fixedconductive member as in the conventional technique. This can prevent thevalve device from becoming oversized and complicated.

The first conductive member may define a circumferential wall extendingin an axial direction of the valve shaft. The circumferential wall mayface the coil spring over a whole area from one end to another end ofthe coil spring in an axial direction of the coil spring.

In this configuration, the coil spring and the first conductive memberface each other over a large area. Due to this, the electrostaticcapacitance between the coil spring and the first conductive membergreatly changes when the valve body and the valve shaft rotate. This canensure that an output value required for determining at least one of therotation angle of the valve body or the rotation angle of the valveshaft is outputted.

The present disclosure discloses a system in which the above valvedevice may be mounted. The system may comprise two power sources. Thevalve device may further comprise a motor configured to be operated bydirect current and rotate the valve shaft. One of the two power sourcesmay be configured to apply a voltage to the motor and another of the twopower sources may be configured to apply a voltage to at least one ofthe coil spring or the first conductive member to generate a potentialdifference between the coil spring and the first conductive member.

This configuration can provide increased accuracy for the detection ofthe rotation angle.

Another valve device disclosed herein may comprise: a valve body; avalve shaft configured to rotate the valve body; a coil spring beingelectrically conductive and configured to be twisted with rotation ofthe valve body and the valve shaft; and a second detector configured todetect at least one of a rotation angle of the valve body or a rotationangle of the valve shaft based on an inductance of the coil spring, theinductance changing according to a state of the coil spring that changeswith the rotation of the valve body and the valve shaft.

This configuration enables detection of at least one of the rotationangle of the valve body or the rotation angle of the valve shaft byusing a change in the inductance of the coil spring in response torotation of the valve body and the valve shaft. In realizing theconfiguration for determining the rotation angle in the valve device,the above configuration enables detection of the rotation angle by usingthe coil spring that is twisted with the rotation of the valve body andthe valve shaft without any additional configurations such as the rotaryconductive member and the fixed conductive member as in the conventionaltechnique. This can prevent the valve device from becoming oversized andcomplicated.

The valve device may further comprise at least one second conductivemember being electrically conductive and arranged on at least one of: aninner side relative to an inner circumferential surface of the coilspring or an outer side relative to an outer circumferential surface ofthe coil spring in a radial direction of the coil spring.

In this configuration, the at least one second conductive memberfunctions as a core of the coil spring, which can ensure that the outputvalue for determining at least one of the rotation angle of the valvebody or the rotation angle of the valve shaft is outputted.

The at least one second conductive member may define a circumferentialwall extending in an axial direction of the valve shaft. Thecircumferential wall may face the coil spring over a whole area from oneend to another end of the coil spring in an axial direction of the coilspring.

In this configuration, the coil spring and the at least one secondconductive member face each other over a large area. Due to this, theelectrostatic capacitance between the coil spring and the at least onesecond conductive member greatly changes when the valve body and thevalve shaft rotate. This can ensure that the output value fordetermining at least one of the rotation angle of the valve body or therotation angle of the valve shaft is outputted.

The present disclosure discloses a system in which the other valvedevice may be mounted. The system may comprise two power sources. Thevalve device may further comprise a motor configured to be operated bydirect current and to rotate the valve shaft. One of the two powersources may be configured to apply a voltage to the motor and another ofthe two power sources may be configured to apply a voltage to at leastone of the coil spring or the at least one second conductive member togenerate a potential difference between the coil spring and the at leastone second conductive member.

This configuration can provide increased accuracy for the detection ofthe rotation angle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a valve device of a firstembodiment.

FIG. 2 is a perspective view of a part of the valve device of the firstembodiment.

FIG. 3 is a cross-sectional view of a part of the valve device of thefirst embodiment.

FIG. 4 is a perspective view of a coil spring of the first embodiment.

FIG. 5 is a diagram showing a graph T of the first embodiment.

FIG. 6 is a cross-sectional view of a part of a valve device of a secondembodiment.

FIG. 7 is a cross-sectional view of a part of a valve device of anotherembodiment.

DETAILED DESCRIPTION

Representative, non-limiting examples of the present disclosure will nowbe described in further detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing aspects of the presentteachings and is not intended to limit the scope of the presentdisclosure. Furthermore, each of the additional features and teachingsdisclosed below may be utilized separately or in conjunction with otherfeatures and teachings to provide improved valve devices, as well asmethods for using and manufacturing the same.

Moreover, combinations of features and steps disclosed in the followingdetailed description may not be necessary to practice the presentdisclosure in the broadest sense, and are instead taught merely toparticularly describe representative examples of the present disclosure.Furthermore, various features of the above-described and below-describedrepresentative examples, as well as the various independent anddependent claims, may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

First Embodiment

A valve device 2 of a first embodiment will be described. As shown inFIG. 1, the valve device 2 includes a casing 10, a valve body 30, and amotor 50. The valve device 2 shown in FIG. 1 is, for example, mounted onan automobile with an engine. The valve device 2 is, for example,disposed on an intake passage through which air to be suctioned into theengine of the automobile flows. The valve device 2 is used to control aflow rate of the air flowing through the intake passage. The valvedevice 2 may be called a throttle valve.

The casing 10 of the valve device 2 includes a housing unit 12 and apassage unit 11. The housing unit 12 houses a first gear 41, a pluralityof second gears 42, the motor 50, and a coil spring 20 to be describedlater. The passage unit 11 of the casing 10 constitutes a part of theintake passage through which the air to be suctioned into the engine ofthe automobile flows. The passage unit 11 has a substantiallycylindrical shape. The air flows along an axial direction of thecylindrical passage unit 11 (direction perpendicular to a sheet surfaceof FIG. 1). The valve body 30 is disposed inside the passage unit 11.

The valve body 30 has a substantially disk shape. The valve body 30 isfixed to a valve shaft 31. The valve shaft 31 extends in a radialdirection of the passage unit 11 (direction orthogonal to the axialdirection of the passage unit 11). The valve shaft 31 is supportedrotatably by a bearing 32 fixed to the casing 10. The valve body 30rotates with rotation of the valve shaft 31. The valve body 30 changes across-sectional area inside the passage unit 11 (passage area of theintake passage) by rotating inside the passage unit 11. The change inthe passage area of the intake passage changes the flow rate of the airflowing through the intake passage. For example, when the valve body 30rotates forward, the passage area increases and the air flow rateincreases. Further, when the valve body 30 rotates in reverse, thepassage area decreases and the air flow rate decreases. The air flowrate changes based on a rotation angle of the valve body 30.

The first gear 41 is fixed to an end 33 of the valve shaft 31. The firstgear 41 is mechanically connected to a rotary shaft 51 of the motor 50via the plurality of second gears 42. When the rotary shaft 51 of themotor 50 rotates, the second gears 42 and the first gear 41 rotate. Whenthe first gear 41 rotates, the valve shaft 31 and the valve body 30rotate. The motor 50 is configured to be operated by direct current androtate the valve shaft 31.

As shown in FIGS. 2 and 3, the first gear 41 includes a shaft portion61, an inner guide 62 (example of a first conductive member), and a gear63. The first gear 41 is constituted of a conductor such as metal orconductive resin. The conductor is electrically conductive. The shaftportion 61 is fixed to the valve shaft 31 via a fastener 65. The innerguide 62 is fixed to the shaft portion 61. The gear 63 is fixed to theinner guide 62. The gear 63 of the first gear 41 is connected to therotary shaft 51 of the motor 50 via the plurality of second gears 42(see FIG. 1).

The inner guide 62 of the first gear 41 is disposed around the valveshaft 31. The inner guide 62 has a substantially cylindrical shape. Theinner guide 62 surrounds the valve shaft 31. The inner guide 62 isdisposed coaxially with the valve shaft 31. The inner guide 62 extendsin an axial direction of the valve shaft 31. A portion of the innerguide 62 facing the coil spring 20 is constituted as a conductivemember. The coil spring 20 is disposed around the inner guide 62. Theinner guide 62 faces an inner circumferential surface 24 of the coilspring 20 over an area from one end to the other end of the coil spring20 in an axial direction of the coil spring 20. The inner guide 62 facesthe inner circumferential surface 24 of the coil spring 20 over a wholearea of the coil spring 20 in the axial direction. In other words, theinner guide 62 defines a circumferential wall extending in the axialdirection of the valve shaft 31. The circumferential wall (inner guide62) is disposed to face the coil spring 20 over the whole area of thecoil spring 20 from its one end to the other end in the axial direction.

The coil spring 20 is wound around the inner guide 62. The coil spring20 surrounds the valve shaft 31 and the inner guide 62. The coil spring20 is disposed coaxially with the valve shaft 31 and the inner guide 62.The coil spring 20 is constituted of a conductor such as metal orconductive resin. The conductor is electrically conductive. The coilspring 20 is configured of a wound conductor wire. The innercircumferential surface 24 of the coil spring 20 faces an outercircumferential surface 64 of the inner guide 62 in a radial directionof the coil spring 20. The inner circumferential surface 24 of the coilspring 20 is at a position separated from the outer circumferentialsurface 64 of the inner guide 62. A clearance is defined between theinner circumferential surface 24 of the coil spring 20 and the outercircumferential surface 64 of the inner guide 62. The coil spring 20being the conductive member and the inner guide 62 being the conductivemember constitute a capacitor by facing each other.

As shown in FIG. 4, the coil spring 20 includes a fixed abutment portion21 and a rotary abutment portion 22. The fixed abutment portion 21 isdisposed at one end of the coil spring 20 and the rotary abutmentportion 22 is disposed at the other end thereof. The fixed abutmentportion 21 abuts a first abutment portion 71. The first abutment portion71 is disposed on an inner surface of the casing 10 housing the coilspring 20 (not shown). Forward rotation of the coil spring 20 (forexample, counter-clockwise rotation) is restricted by the fixed abutmentportion 21 coming into abutment with the first abutment portion 71.

The rotary abutment portion 22 at the other end of the coil spring 20abuts a second abutment portion 72. The second abutment portion 72 isdisposed on an outer surface of the first gear 41 housed in the casing10 (not shown). Reverse rotation of the coil spring 20 (for example,clockwise rotation) is restricted by the rotary abutment portion 22coming into abutment with the second abutment portion 72. When the firstgear 41 rotates forward, the rotary abutment portion 22 comes intoabutment with the second abutment portion 72.

When the first gear 41 rotates, the coil spring 20 is thereby twisted.When the first gear 41 rotates forward, the coil spring 20 is twisted ina forward rotation direction (for example, counter-clockwise). When thefirst gear 41 rotates in reverse, this twist in the coil spring 20 isreleased. When the coil spring 20 is twisted, a diameter of the coilspring 20 decreases. When the diameter of the coil spring 20 decreases,a distance H between the inner circumferential surface 24 of the coilspring 20 and the outer circumferential surface 64 of the inner guide 62becomes shorter (see FIG. 3). Further, when the coil spring 20 istwisted, a length L of the coil spring 20 in the axial direction becomeslonger. When the length L of the coil spring 20 in the axial directionbecomes longer, the area over which the inner circumferential surface 24of the coil spring 20 faces the outer circumferential surface 64 of theinner guide 62 becomes larger.

As shown in FIG. 3, the valve device 2 includes a CV circuit 80 and anengine control unit (ECU) 100.

The CV circuit 80 is connected to the coil spring 20 and the inner guide62 of the first gear 41. The CV circuit 80 is a circuit configured tooutput a voltage value depending on an electrostatic capacitance of acapacitor to which the CV circuit 80 is connected. The electrostaticcapacitance of a capacitor is generally proportional to an area overwhich a pair of conductive members faces each other, and is inverselyproportional to a distance between this pair of conductive members. Thecoil spring 20 and the inner guide 62 of the valve device 2 constitute acapacitor. The CV circuit 80 outputs a voltage value depending on theelectrostatic capacitance between the coil spring 20 and the inner guide62 (that is, the electrostatic capacitance of the capacitor). Since theCV circuit 80 is incorporated in a known CV converter, a detaileddescription thereof will be omitted.

The ECU 100 is configured to execute processes and control related tothe valve device 2. The ECU 100 includes a memory 120. The ECU 100 isconfigured to determine the rotation angle of the first gear 41, thevalve shaft 31, and the valve body 30 based on the voltage valueoutputted from the CV circuit 80. As shown in FIG. 5, the ECU 100stores, in advance in the memory 120, a graph T indicating arelationship between the voltage value and the rotation angle of thefirst gear 41, the valve shaft 31, and the valve body 30. The ECU 100uses the graph T stored in the memory 120 to determine the rotationangle of the first gear 41, the valve shaft 31, and the valve body 30based on the voltage value outputted from the CV circuit 80. The graph Tis obtained in advance by experiments and/or analyses. For example, thegraph T is created in advance by determining a relationship between therotation angle exhibited when the first gear 41, the valve shaft 31, andthe valve body 30 rotate and the voltage value outputted from the CVcircuit 80 in response to the rotation thereof by experiments. The graphT created as such is stored in the memory 120.

Next, an operation of the valve device 2 will be described. In the valvedevice 2 as above, the first gear 41, the valve shaft 31, and the valvebody 30 rotate (forward or in reverse) when the rotary shaft 51 of themotor 50 rotates (forward or in reverse).

When the first gear 41, the valve shaft 31, and the valve body 30 rotateforward, the coil spring 20 is thereby twisted circumferentially in theforward rotation direction. When the coil spring 20 is twisted in theforward rotation direction, the diameter of the coil spring 20decreases. That is, the inner circumferential surface 24 of the coilspring 20 approaches the outer circumferential surface 64 of the innerguide 62, by which the distance H between the coil spring 20 and theinner guide 62 becomes shorter. As a result, the electrostaticcapacitance between the coil spring 20 and the inner guide 62 becomeslarger. Further, when the coil spring 20 is twisted in the forwardrotation direction, the length L of the coil spring 20 in the axialdirection becomes longer. That is, the area over which the innercircumferential surface 24 of the coil spring 20 faces the outercircumferential surface 64 of the inner guide 62 increases. As a result,the electrostatic capacitance between the coil spring 20 and the innerguide 62 becomes larger. The larger the rotation angle of the first gear41, the valve shaft 31, and the valve body 30 is, the larger theelectrostatic capacitance between the coil spring 20 and the inner guide62 becomes.

When the first gear 41, the valve shaft 31, and the valve body 30 rotatein reverse, the twist of the coil spring 20 is released. When the twistof the coil spring 20 is released, the diameter of the coil spring 20becomes larger. That is, the inner circumferential surface 24 of thecoil spring 20 moves away from the outer circumferential surface 64 ofthe inner guide 62, by which the distance H between the coil spring 20and the inner guide 62 becomes longer. As a result, the electrostaticcapacitance between the coil spring 20 and the inner guide 62 becomessmaller. Further, when the twist of the coil spring 20 is released, thelength L of the coil spring 20 in the axial direction becomes shorter.That is, the area over which the inner circumferential surface 24 of thecoil spring 20 faces the outer circumferential surface 64 of the innerguide 62 decreases. As a result, the electrostatic capacitance betweenthe coil spring 20 and the inner guide 62 becomes smaller.

The ECU 100 determines the rotation angle of the valve body 30 and thevalve shaft 31 based on the electrostatic capacitance that changesbetween the coil spring 20 and the inner guide 62 in response to therotation of the valve body 30 and the valve shaft 31. More specifically,the CV circuit 80 connected to the coil spring 20 and the inner guide 62outputs a voltage value depending on the electrostatic capacitancebetween the coil spring 20 and the inner guide 62 when the coil spring20 is not twisted or the electrostatic capacitance therebetween when thecoil spring 20 is twisted. Then, based on the voltage value outputtedfrom the CV circuit 80, the ECU 100 determines the rotation angle of thefirst gear 41, the valve shaft 31, and the valve body 30. The ECU 100determines the rotation angle of the first gear 41, the valve shaft 31,and the valve body 30 according to the graph T (see FIG. 5) stored inthe memory 120. Due to this, the ECU 100 corresponds to a firstdetector.

(Effects)

The valve device 2 of the first embodiment has been described above. Asit is apparent from the above disclosure, the valve device 2 includesthe coil spring 20 configured to be twisted with the rotation of thefirst gear 41, the valve shaft 31, and the valve body 30, and the innerguide 62 being the conductive member that faces the innercircumferential surface 24 of the coil spring 20 in the radial directionof the coil spring 20. Further, the valve device 2 includes the ECU 100configured to determine the rotation angle of the first gear 41, thevalve shaft 31, and the valve body 30 based on the voltage valuedepending on the electrostatic capacitance between the coil spring 20and the inner guide 62 exhibited when the coil spring 20 is twisted withthe rotation of the first gear 41, the valve shaft 31, and the valvebody 30.

This configuration enables the determination of the rotation angle ofthe first gear 41, the valve shaft 31, and the valve body 30 by usingthe existing configuration. That is, the configuration can provide thefunction of detecting the rotation angle to the valve device 2 whilepreventing the valve device 2 from becoming oversized and complicated.

In the above valve device 2, the inner guide 62 is disposed to face thecoil spring 20 over the whole area from the one end to the other end ofthe coil spring 20 in the axial direction of the coil spring 20. In thisconfiguration, the area over which the coil spring 20 faces the innerguide 62 is large. As such, the electrostatic capacitance between thecoil spring 20 and the inner guide 62 greatly changes upon when the coilspring 20 is twisted, by which accuracy for determining the rotationangle can be increased.

One embodiment has been described above, however, specific aspects arenot limited to the above embodiment. In the description below, the samereference signs will be given to configurations identical to those inthe foregoing disclosure, and description thereof will be omitted.

Second Embodiment

As shown in FIG. 6, a valve device 2 of a second embodiment includes anLV circuit 90 instead of the CV circuit 80. The LV circuit 90 isconnected to the one and the other ends of the coil spring 20 in theaxial direction. The LV circuit 90 is a circuit configured to output avoltage value depending on an inductance of a coil to which the LVcircuit 90 is connected. The inductance of a coil is generallyproportional to the square of the number of turns of the coil. The LVcircuit 90 outputs a voltage value depending on an inductance of thecoil spring 20. The ECU 100 is configured to determine the rotationangle of the first gear 41, the valve shaft 31, and the valve body 30based on the voltage value outputted from the LV circuit 90. Since theLV circuit 90 is incorporated in a known LV converter, a detaileddescription thereof will be omitted.

In the valve device 2 of the second embodiment, when the first gear 41,the valve shaft 31, and the valve body 30 rotate forward, the coilspring 20 is thereby circumferentially twisted in the forward rotationdirection. When the coil spring 20 is twisted in the forward rotationdirection, the number of turns of the coil spring 20 increases. When thenumber of turns of the coil spring 20 increases, the inductance of thecoil spring 20 becomes larger proportional to the square of the numberof turns. The larger the rotation angle of the first gear 41, the valveshaft 31, and the valve body 30 is, the larger the inductance of thecoil spring 20 becomes.

As such, the ECU 100 determines the rotation angle of the valve body 30and the valve shaft 31 based on the inductance of the coil spring 20that changes with the rotation of the valve body 30 and the valve shaft31. More specifically, the LV circuit 90 connected to the coil spring 20outputs a voltage value depending on the inductance of the coil spring20 when the coil spring 20 is not twisted or the inductance of the coilspring 20 when the coil spring 20 is twisted. Further, the ECU 100determines the rotation angle of the first gear 41, the valve shaft 31,and the valve body 30 based on the voltage value outputted from the LVcircuit 90. The ECU 100 determines the rotation angle of the first gear41, the valve shaft 31, and the valve body 30 based on the graph T (seeFIG. 5) stored in the memory 120. Due to this, the ECU 100 correspondsto a second detector.

(Effects)

The second embodiment has been described above. As it is apparent fromthe above description, the valve device 2 of the second embodiment candetermine the rotation angle of the first gear 41, the valve shaft 31,and the valve body 30 by using the existing configuration. That is, thefunction of detecting the rotation angle can be provided to the valvedevice 2, while the valve device 2 is prevented from becoming oversizedand complicated.

Further, the above valve device 2 includes the inner guide 62 (anexample of a second conductive member) arranged on an inner siderelative to the inner circumferential surface 24 of the coil spring 20in the radial direction of the coil spring 20. The inner guide 62functions as a core of the coil. This configuration ensures that theoutput value for determining the rotation angle is outputted.

Other Embodiments

(1) In another embodiment, the inner guide 62 of the first gear 41 maynot face the inner circumferential surface 24 of the coil spring 20 overthe area from the one end to the other end of the coil spring 20 in theaxial direction. The inner guide 62 may not face the innercircumferential surface 24 of the coil spring 20 over the whole area ofthe coil spring 20 in the axial direction. The inner guide 62 may faceat least a part of the inner circumferential surface 24 of the coilspring 20.

(2) In another embodiment, metal plating may be applied on the outercircumferential surface 64 of the inner guide 62 of the first gear 41.The outer circumferential surface 64 of the inner guide 62 may be coatedby a metal film. Alternatively, the outer circumferential surface 64 ofthe inner guide 62 may be covered by a metal plate. The metal film orthe metal plate may be another example of the first conductive member.In this configuration, the capacitor is constituted of the coil spring20 and one of the metal film and the metal plate.

(3) In the first embodiment as above, the inner guide 62 facing theinner circumferential surface 24 of the coil spring 20 is an example ofthe first conductive member, however, no limitation is made to thisconfiguration. In another embodiment, as shown in FIG. 7, the valvedevice 2 may include an outer guide 66 facing an outer circumferentialsurface 25 of the coil spring 20. The outer guide 66 is constituted of aconductor such as metal or conductive resin. The outer guide 66 may beanother example of the first conductive member. The capacitor may beconstituted of the coil spring 20 and the outer guide 66. The outercircumferential surface 25 of the coil spring 20 and an innercircumferential surface 67 of the outer guide 66 face each other. The CVcircuit 80 is connected to the coil spring 20 and the outer guide 66(not shown). The CV circuit 80 outputs a voltage value depending on anelectrostatic capacitance between the coil spring 20 and the outer guide66. This configuration can ensure that the output value for determiningthe rotation angle is outputted with a simple configuration, as well.Only a portion of the outer guide 66 facing the coil spring 20 may beconstituted of a conductor such as metal or conductive resin.

(4) In the second embodiment as above, the inner guide 62 facing theinner circumferential surface 24 of the coil spring 20 is an example ofthe second conductive member, however, no limitation is made to thisconfiguration. In another embodiment, the outer guide 66 facing theouter circumferential surface 25 of the coil spring 20 may be an exampleof the second conductive member. One of the inner guide 62 and the outerguide 66 may be an example of the second conductive member. Further,both the inner guide 62 and the outer guide 66 may be examples of thesecond conductive member.

(5) In the above embodiments, the ECU 100 determines the rotation angleof the first gear 41, the valve shaft 31, and the valve body 30according to the graph T stored in the memory 120, however, nolimitation is made to this configuration. In another embodiment, the ECU100 may determine the rotation angle of the first gear 41, the valveshaft 31, and the valve body 30 according to a predetermined conversionequation. Similar to the graph T, the predetermined conversion equationindicates a relationship between the voltage value and the rotationangle.

(6) In the above embodiments, the valve device 2 is employed in theautomobile, however, no limitation is made to this configuration. Inanother embodiment, the valve device 2 may be employed in machines ordevices other than automobiles.

(7) In another embodiment, the valve device 2 may include, instead ofthe CV circuit 80, a circuit (not shown) configured to output a value ofthe electrostatic capacitance between the coil spring 20 and the innerguide 62 when the coil spring 20 is twisted. The ECU 100 may determinethe rotation angle of the first gear 41, the valve shaft 31, and thevalve body 30 based on this value of the electrostatic capacitanceoutputted from this circuit. That is, the ECU 100 may obtain theelectrostatic capacitance between the coil spring 20 and the inner guide62 from the circuit, and may detect the rotation angle from the obtainedelectrostatic capacitance.

(8) In another embodiment, in a case where a system including the valvedevice 2 includes two or more power sources, one of the power sources(one power source) may apply a voltage to the motor 50 and the other ofthe power sources (the other power source) may apply a voltage to thecoil spring 20 or the inner guide 62 to generate a potential differencebetween them. For example, the coil spring 20 may be connected to theother power source and the inner guide 62 may be connected to theground. Alternatively, the coil spring 20 may be connected to the groundand the inner guide 62 may be connected to the other power source. Inthis configuration, motor noise does not affect the detection of therotation angle, thus accuracy for the detection of the rotation anglecan be increased.

(9) In a variant of the first embodiment, the ECU 100 may include thefunction of the CV circuit 80. In this case, the CV circuit 80 may beomitted. Similarly, in a variant of the second embodiment, the ECU 100may include the function of the LV circuit 90. In this case, the LVcircuit 90 may be omitted.

What is claimed is:
 1. A valve device comprising: a valve body; a valveshaft configured to rotate the valve body; a coil spring beingelectrically conductive and configured to be twisted with rotation ofthe valve body and the valve shaft; a first conductive member beingelectrically conductive and facing an inner circumferential surface oran outer circumferential surface of the coil spring in a radialdirection of the coil spring; and a first detector configured to detectat least one of a rotation angle of the valve body or a rotation angleof the valve shaft based on an electrostatic capacitance between thecoil spring and the first conductive member, the electrostaticcapacitance changing according to a state of the coil spring thatchanges with the rotation of the valve body and the valve shaft.
 2. Thevalve device according to claim 1, wherein the first conductive memberdefines a circumferential wall extending in an axial direction of thevalve shaft, and the circumferential wall faces the coil spring over awhole area from one end to another end of the coil spring in an axialdirection of the coil spring.
 3. A system in which the valve deviceaccording to claim 1 is mounted, the system comprising two powersources, wherein the valve device further comprises a motor configuredto be operated by direct current and rotate the valve shaft, and one ofthe two power sources is configured to apply a voltage to the motor andanother of the two power sources is configured to apply a voltage to atleast one of the coil spring or the first conductive member to generatea potential difference between the coil spring and the first conductivemember.
 4. A valve device comprising: a valve body; a valve shaftconfigured to rotate the valve body; a coil spring being electricallyconductive and configured to be twisted with rotation of the valve bodyand the valve shaft; and a second detector configured to detect at leastone of a rotation angle of the valve body or a rotation angle of thevalve shaft based on an inductance of the coil spring, the inductancechanging according to a state of the coil spring that changes with therotation of the valve body and the valve shaft.
 5. The valve deviceaccording to claim 4, further comprising: at least one second conductivemember being electrically conductive and arranged on at least one of: aninner side relative to an inner circumferential surface of the coilspring or an outer side relative to an outer circumferential surface ofthe coil spring in a radial direction of the coil spring.
 6. The valvedevice according to claim 5, wherein the at least one second conductivemember defines a circumferential wall extending in an axial direction ofthe valve shaft, and the circumferential wall faces the coil spring overa whole area from one end to another end of the coil spring in an axialdirection of the coil spring.
 7. A system in which the valve deviceaccording to claim 5 is mounted, the system comprising two powersources, wherein the valve device further comprises a motor configuredto be operated by direct current and to rotate the valve shaft, and oneof the two power sources is configured to apply a voltage to the motorand another of the two power sources is configured to apply a voltage toat least one of the coil spring or the at least one second conductivemember to generate a potential difference between the coil spring andthe at least one second conductive member.